Data Compression

Compression- The process of reducing the number of bits required to represent data

• There are many reasons why files can get extremely large. This could be high resolution images or video, for example
• In order to reduce storage requirements and make it quicker to transmit these files, they are often compressed

• There are several methods for compressing data depending on the type of data being encoded.
• For example, we can zip a file or reduce a high resolution image to low resolution.

Lossless- Means that the compressed file is as accurate as it was before (so no data lost)]

Lossy- Means that there will be some degradation in the data e.g. grainier image produced

Run-Length Encoding

• A method of compressing data by eliminating repeated data
• E.G. [F][F][F][F][F] = 5F (Next 5 pixels are F]

Dictionary Encoding

• A method of compressing text files. This works on the principle that within text there will be common strings of characters. Rather than rewriting these same strings they can be coded in some way.

• There is a limit to how small you can reduce a file with lossless compression
• If memory is an issue or network transmission speed, you will need to make a file smaller
• This is often the case with streaming audio or video. In these cases, a compression technique that leads to some degradation in data quality may be acceptable
• The widespread use of mobile data on various portable devices means that lossy compression is used, even though it leads to a degradation of the original data.

• Lossy Compression works by identifying data that can be removed, while still creating an acceptable representation
• The user often has control over the amount of compression which is used.